Related art head-mounted display apparatuses (so-called “head-mounted displays (HMDs)”) include display devices worn on the head of individual users. The head-mounted display apparatuses are designed to lead light from displayed images and light from the external world to the eyes of the individual wearers to provide the wearers with imagery of the images and the external world.
Such head-mounted display apparatuses may be an example of an apparatus configured to allow users to see optically superimposing surrounding scenery on images displayed on a pair of small displays via an optical system composed of a pair of reflective mirrors, a pair of eye pieces, and a polarization beam splitter. Such an apparatus includes a dimmer filter configured to change the transmittance, which is disposed in front of the polarization beam splitter (e.g., Patent Document 1).